Method and apparatus for producing a detonating cord

Abstract

An improved low-energy detonating cord, which is light-weight, flexible, strong, and non-conductive, detonates at high velocity, and is readily adapted to high-speed continuous manufacturing techniques, has a continuous solid core of a deformable bonded detonating explosive composition comprising a crystalline high explosive compound, preferably superfine PETN, admixed with a binding agent, the crystalline explosive loading being about from 0.5 to 10 grains per foot (0.1 to 2 grams per meter) of length; and, enclosing the core, a protective plastic sheath, e.g., about 0.005-0.075 inch (0.127-1.905 mm) thick, no metal or woven textile layers being present around the core or sheath. Perferably, one or more continuous strands of reinforcing yarn, e.g., running substantially parallel to the core's longitudinal axis, are located between the core and the plastic sheath, or in or around the sheath. A preferred cord can be made by drawing strands of yarn under tension in the form of a moving cage of substantially parallel strands, allowing the moving cage to engrain a bonded explosive core within it and thereby form a conveyor for the core, and applying a layer of plastic material around the cage while effecting substantially no change in the diameter of the exposive core after its entrainment within the cage.

I claim: 
     
       1. A method of producing a detonating cord comprising (a) forming a mixture of cap-sensitive crystalline high explosive compound and a binding agent therefor into a continuous solid core;   (b) drawing strands of yarn under tension sufficient to form a moving cage of substantially parallel longitudinal strands;   (c) allowing said moving cage to entrain said core within it, whereby said cage becomes a conveyor for said core;   (d) applying a layer of soft plastic material around said moving cage while effecting substantially no change in the diameter of said core after its entrainment within said cage; and   (e) hardening the plastic material.   
     
     
       2. A method of claim 1 wherein said core is extruded into said moving yarn cage, and said caged core unit subsequently passes into and through an extrusion die wherein said plastic material is formed into a sheath over said caged core unit. 
     
     
       3. A method of claim 2 wherein said die is a tubular die and the plastic tube formed therein is collapsed onto said caged core unit by the drawing of a vacuum through said die. 
     
     
       4. A method of claim 1 wherein said strands of yarn and said core are moved separately into an extrusion die wherein said strands are formed into said cage and entrain said core, and said plastic sheath forms around said caged core unit by passage of said caged core unit through a stream of plastic. 
     
     
       5. A method of claim 1 wherein said mixture is formed into said solid core under vacuum. 
     
     
       6. A method of claim 1 wherein said mixture is treated so as to exclude from the core particles larger than about 25% of the core diameter. 
     
     
       7. Apparatus for producing a detonating cord comprising (a) a first extrusion means, for forming a mass of a deformable bonded detonating explosive composition into a continuous solid core;   (b) means for orienting strands of yarn substantially parallel to one another in annular array;   (c) means for drawing said substantially parallel strands under tension sufficient to form them into a moving cage, said strand-orienting means being so positioned with respect to said first extrusion means that said cage internally entrains and conveys said core emanating from said first extrusion means;   (d) a second extrusion means, for applying a soft plastic material in the form of a sheath to a substrate moving therethrough, said second extrusion means being so positioned with respect to said first extrusion means and said strand-orienting and strand-drawing means that the caged core is drawn through said second extrusion means by said strand-drawing means so as to constitute the substrate for the sheath application with substantially no previous, coincident, or subsequent reduction in core diameter; and   (e) means adapted to receive the passage of the thus-drawn sheathed, caged core for hardening said plastic material.   
     
     
       8. Apparatus of claim 7 wherein said first extrusion means is associated with an extruder chamber which contains an opening for the drawing of a vacuum. 
     
     
       9. Apparatus of claim 7 wherein said first extrusion means is associated with an extruder chamber which contains particle-screening means for excluding particles larger than about 25% of the core diameter from the core. 
     
     
       10. Apparatus of claim 7 wherein said first extrusion means is associated with a ram extruder provided with a heated chamber. 
     
     
       11. Apparatus of claim 7 including means associated with said first extrusion means and with said strand-drawing means, adapted to sense the output of said first extrusion means and adjust the speed of said strand-drawing means accordingly.